In a turning type of metal cutting operation, a replaceable cutting insert held in a slot located at an end of an insert holder is brought into contact with a rotating metal workpiece, causing metal chips to shear away from a cutting area on the workpiece. The slot comprises a lower and an upper slot surface that abut respectively a bottom and a top surface of the cutting insert. The lower slot surface supports the cutting insert and the upper slot surface is clamped down on the cutting insert to fix it in the slot. The forward end of the slot is open, so that a cutting edge and a rake surface of the cutting insert are exposed for cutting the workpiece and evacuating the chips.
It is necessary for the slot and the cutting insert to include means for accurately positioning the cutting insert at a selected location in the slot during installation, relative to the x, y, and z axes of three-dimensional space, and for minimizing its translational and rotational movement on these axes during cutting. To these ends, three types of abutment that restrain the cutting insert against five of six force vectors that can arise during cutting, the possible vector directions relative to the slot being: vertically up or down, laterally to either side, or longitudinally in or out. The first type of abutment, directed against vertical forces, is provided by the upper slot surface abutting the cutting insert top surface and by the lower slot surface abutting the cutting insert lower surface. The second type of abutment, directed against lateral forces, is provided by mating nonplanar profiles in the same abutting surfaces. The third type of abutment, directed against inward longitudinal force is a stop, such as a pin, at the back of the slot abutting a back surface of the cutting insert. However, no abutment is provided against outward longitudinal force. The only element restraining the cutting insert in the slot in the outward direction is friction between the upper and lower slot surfaces and the respective top and bottom cutting insert surfaces. Hence unwanted outward displacement of the cutting insert from the slot can occur when outwardly-directed force is exerted thereon during cutting operations.
It is known to provide an abutment against outwardly-directed force by forming the forward portions of the abutting lower slot surface and bottom cutting insert surface to have mating nonplanar profiles, similar to, but orthogonal to, those used for abutment against lateral forces. An example is disclosed by Pano and Braun in U.S. Pat. No. 4,938,640 (1990). However, the length of the transverse mating is limited to the width of the cutting insert. Also, the portion of the bottom surface of the cutting insert that is allocated for transverse mating could otherwise be used for longitudinal mating.
In addition to cutting forces, in some cutting operations there is a further constraint that access to the cutting area is restricted. An example of such an operation is an undercut, where material is cut away from the underside of the workpiece to leave an overhang. To operate within this constraint, it is known in the art to form the insert holder with one or more angles before the slot and to form the cutting insert of shorter than standard length. However, the shortened cutting insert has shorter bottom and top surfaces for clamping in the slot, hence it is less stable.
Another solution for cutting where access is restricted is provided by an angled cutting insert, comprising a shaft with a cutting portion projecting integrally from it at an angle, an example of which is disclosed by Hansson and Andersson in U.S. Pat. No. 6,582,163 (2001). The shaft, which can be of standard length, is clamped in the slot. However, the cutting portion is unsupported; therefore forces acting upon it are transferred to the shaft, increasing the torque of the shaft.